Neutron scattering study of human serum low density lipoprotein.

Abstract

Regions of different proton density in the low density lipoprotein (LDL) particle from human serum have been determined by neutron scattering. From measurements in various H20/D20 mixtures, the LDL particle appears to be quasi-spherical, with the centers of gravity of the hydrocarbon and polar regions coinciding. The average volume occupied by a particle was found to be 3.2 X 106 Al, with the volume fraction occupied by the hydrocarbons being 60%. The radius of gyration of the hydrocarbon region was 64 A, while that of the polar region was 100 A. Consequently, the core of LDL is predominantly occupied by the hydrocarbon chains, while the outer shell is sparsely occupied by protein emerging from the lipid core.Human serum lipoproteins are particles in which serum lipids are associated with characteristic polypeptides in discrete species generally defined by their hydrated density (1). In addition to playing a major role in lipid transport and energy metabolism (2), lipoproteins may be involved in the maintenance of cell membranes (3) and in the regulation of lipid biosynthesis (1, 4). The study of lipoproteins is of particular importance because of several diseased states associated with alterations in their concentration and/or structure (5).Low density lipoproteins (LDL) are the predominant species in the density range 1.019-1.063 g/ml in human serum (1-4).These particles, which appear to be roughly spherical in shape (6, 7) and to have an average molecular weight of 2 to 3 X 106 (8), are thought to be complex associations of 21% protein, 22% phospholipids, 8% free cholesterol, 37% cholesterol esters, and 11% triglycerides (1-4). How these lipid and protein components are arranged in LDL remains elusive, although several models have been suggested (6,7,(9)(10)(11) The wavelength spectrum was centered at 3.7 A and had a total half width of 1.7 A. The correction of the neutron scattering curves for the influence of this broad wavelength distribution turned out to be inadequate. It resolved quite clearlv the maxima of the curves (Fig. 1); however, the depth of the minima often remained quite inaccurate.In order to cover a sufficiently broad range of scattering angles we placed the detector at 0.66, 2, and 10 m from the sample. The neutron flux passing the sample area of 2 cm2 varied from 106 to 108 neutrons/'s depending on the angular resolution. 2270Abbreviation: LDL, low density lipoprotein.

The Structure of Human‐Plasma Low‐Density Lipoprotein B

“…The results of both Tardieu et a/. [15] and Stuhrmann et al [18] were in strong contrast to the previously postulated spherical lipid bilayer model of Mateu et al [13] with some protein in the center of the particle, and also to the model based upon NMR spectroscopic data by Finer et nl. [19].…”

Anomalous dispersion of small-angle scattering of horse-spleen ferritin at the ironKabsorption edge

“…This is the dependence of R on /) in real contrast variation (Stuhrmann, Tardieu, Mateu, Sardet, Luzzati, Aggerbeck & Scanu, 1975). The same coefficients Rc, a and fl can be determined if anomalous scatterers are in the solvent only:…”

The Structure of 11‐S Globulins from Sunflower and Rape Seed

“…The desmeared scattering curve Z(s) was extrapolated to larger scattering angles according to the equation lim s4Z(s) = A + B . s4 (2) S + C C and the constant B was subtracted from I(s) [15,16] have shown, however, that the termination effect on D ( x ) of 11-S globulin at smaX > 1.6 nm-' come within the error limits of D ( x ) .…”